Have you ever tried to 'nag' someone into obedience? It doesn't work well, does it? In the long run, one or both of you will come to have ill feelings toward the other. Nagging doesn't change behavior - it might even intensify it as the other seeks to magnify the 'annoyance' the disobedience brings you! We all do things we shouldn't do from time to time - we are all human, all have a sin nature, and all think way too highly of our 'self' at times. It is 'when', not 'if' we do something wrong, because we will all eventually find ourselves in need of a helping hand to be free of whatever it is we are struggling to overcome. Notice, it is a helping hand God asks us to bring, not the conviction of criticism, annoyance of nagging, or condemnation of shame.
Gentleness is key to helping one trapped in the downward spiral of sin. Foolish behavior seldom just goes away - it requires consistent change, and that change is only possible when Christ is the driving force within that change. What happens when we go to a person who is making foolish decisions, attempting to persuade them otherwise with a whole lot of 'opinion' as to why their decisions are wrong? They frequently reject such 'advice' as 'not applicable' to their circumstances, don't they? They cannot see that our 'opinions' matter all that much because 'their circumstances are different'. Nagging won't do the other person any good and may even drive a wedge that splits the relationship we had with that individual.
Christ asks us to come alongside - be gentle, not critical. Be open to hearing their heart and sharing in their hurt. Take those troubling things to God on their behalf. In other words, do 'warfare' in the spiritual realm when they aren't up to the fight themselves. We each have so much to offer one another, but it must be done in a loving, caring manner. It cannot be motivated by selfish ambition or pride but must be with humble spirit. When we care for each other in a loving, compassionate manner, we are opening the door for Christ to heal hurts and set paths straight once again. Sometimes we will be able to give advice, but what another does with it is their choice. We can never fill the place or position of the Holy Spirit in their lives. He will help with the choice - we stand alongside and pray them through to the other side of that choice! Just sayin!